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CH...N    CO

Caffeine (Trimethyl xanthine),        CO C    N(CI 1,)

CH...N    C-  N ,'yCI1

Digest the tea with 500 c.c. boiling water for a. quarter of an
hour, and filter through cloth into a basin placed over a ring-
burner (see p. 108), so that the liquid in the filter is kept hot.
Moderately line unsized cotton cloth is used, and is wetted and
stretched on a wooden frame as shown in Kig. '/S- Wash with
a further 250 c.c. of boiling water. Add to the. iiltrate a, solu-
tion of basic lead acetate (made by boiling acetate of lead
solution with excess of litharge, and then filtering) until no more

precipitate is formed. Killer hot through a large lluted filter
froiM precipitated albumin, and wash with water. To thr boil 
ing filtrate add dilute sulphuric acid until the le'id is precipitated
as sulphate. Kilter or de-cant from the sulphate of le;ul, and
concentrate the solution with the addition of animal charcoal
to 250 300 c.c. Miter and extract the filtrate three times witb
small quantities (50 c.c.) of chloroform. Distil off the chloro-
form on the water-bath, and dissolve the residue in a. small
quantity of hot water. On allowing (he solution to evaporate
very slowly, long silky needles of caffeine separate, which may
have a slightly yellow tint, in which case they should be drained,
re-dissolved in water, and boiled with the addition of animal
charcoal. The needles contain one molecule of water, which
they lose at 100 and melt at 234*5". Meld about rf; grams.
See Appendix, p. 269.